Prior techniques for manufacturing shaped rods with a hollow cross section by using a mandrel are described for example in U.S. application 3,966,388 and FR-A-2,312,356, as well as French patent application EN. 86/05.093, which relates to a support for molding several rods simultaneously.
Industrial use of these techniques, however, lacks flexibility of the manufacturing device, as manifested primarily by irregular feed of the mold support to the mandrel, with this negative factor being intensified when the rate of manufacture and/or the length of the mandrel increase.
The length of the mandrel depends on the time required to stabilize the material of which the rods are made. In general, this length increases directly with the rotational speed of the mandrel, itself a direct function of the rate of manufacture.
Using a long stabilizing oven allows material to be used that stabilizes slowly, such as non-reactive resins, thus making it possible to benefit from numerous advantages associated with this material, such as pre-cross-linking.
This irregular feed is accompanied by jamming of the support and/or the shaped material as the support is wound on the mandrel, during its travel, or during its removal.
These jams can cause deformation of the sections and especially of the bent rods, which imposes harmful restraints on their use, especially when they are finally installed, for manufacturing tubing.